Reusable warmers of the type employing a super-cooled solution and an activator

ABSTRACT

The present invention provides reusable warmers of the supersaturated solution type that are substantially free of saddlebagging. The warmers also exhibit a more sustained period of time during which the heat pack remains within a therapeutically useful temperature range. The reusable warmers of the present invention also maintain a substantial degree of flexibility during their useful heat cycle. The reusable warmers comprise a flexible container, and located within said container, a supercooled salt solution, an activator for initiating crystallization of said supercooled salt solution, and a gelling agent, said gelling agent being present in sufficient quantity to convert said salt solution to a gel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.538,838, filed Jun. 15, 1990 now U.S. Pat. No. 5,058,563.

FIELD OF THE INVENTION

This invention relates to reusable warmers for directly applying heat toareas of the human body to relieve muscle aches, pains and the likewhich employ a super-cooled aqueous solution (as for example, asuper-cooled, super-saturated aqueous sodium acetate solution) and anactivator to initiate the crystallization of the super-cooled liquid.

BACKGROUND OF THE INVENTION

Reusable warmers employing a super-cooled aqueous solution and anactivator have been used by sportsmen and others for years to warm partsof the human body. Such a reusable warmer is shown, for example, in U.S.Pat. No. 4,077,390 to Stanley et al. (issued Mar. 7, 1978) generally atFIG. 1 and described generally at column 1 line 59.Iadd., .Iaddend.tocolumn 2.Iadd., .Iaddend.line 4.Iadd., .Iaddend.as being a sealedbag-like flexible receptacle (such as polyethylene, nylon and the like)containing a super-cooled aqueous sodium acetate and an activatorcomprising a flexible metal strip having one or more slits or fissures,said patent being incorporated herein by reference. A reusable warmerhaving another type of activator is described in U.S. Pat. No. 4,872,442to Manker (issued Oct. 10, 1989), said patent being incorporated hereinby reference.

In reusable warmers of the present type, a super-cooled solution, suchas an aqueous sodium acetate solution, is contained in a flexiblereceptacle, such as a bag-like receptacle. The solution is activated byflexing or bending the activator strip. Upon activation, the sodiumacetate in the super-cooled solution crystallizes and heat (i.e. the"heat of crystallization") is evolved. All references herein to reusablewarmer or heat packs are meant to refer to the aforementioned type ofheat pack in which a .[.supercooled.]. .Iadd.super-cooled.Iaddend.solution is provided in a flexible container, which also housesa trigger or activator for initiating crystallization.

One of the primary uses for such reusable warmers is the application ofheat directly to various parts of the human body for therapeuticpurposes such as to relieve muscle aches and pains, to reduceinflammation and to promote healing of damaged tissue. Other usesinclude those by sports participants (such as hunters, skiers and thelike) or sports enthusiasts (such as spectators at sporting events) whouse the warmers to keep various parts of their bodies warm during coldweather.

Unfortunately, because the .[.supercooled.]. .Iadd.super-cooled.Iaddend.solution used in the warmer is water-like in consistency, it iseasily drawn by gravity. The resultant flowing of the solution presentsa practical problem in applying the warmer to the human body. A personusing a reusable warmer may be standing, sitting or walking, whiletrying to apply the warmer. The gravitational pull on the fluid,however, causes the solution to flow to the lowest possible point,making application difficult, if not impossible under such conditions.

Further, because the human body, in general, is contoured and not flat,attempts to apply the present day warmers to areas such as the knee,even when the patient is in a horizontal position, present greatdifficulty. Because some portion of the region to be treated always willremain in a nonhorizontal position (i.e. not flat), the liquid naturallyflows away therefrom.

In particular, it has been found that during use the super-cooledaqueous solution in the present-day, reusable warmers .[.the supercooledliquid in the plastic bag.]. will flow, for example, around a leg or armor knee, from areas in the bag having too much solution, leaving otherareas with too little. This phenomenon has been referred to as"saddlebagging."

Saddlebagging leads to uneven coverage by the reusable warmer of thebody part area to be heated. Heretofore, the art has attempted tominimize saddlebagging by various means. These have included, forexample, adding welds to the flexible, sealed container of the warmer sothat the solution is restrained from freely flowing. Also the use ofvery heavy gauge plastics which will not only be more resistant tobending, but will also act to restrain flow of the super-cooled solutionand keep a more flat surface have been tried.

None of the aforementioned solutions to the saddlebagging problem hasproven satisfactory, since they render the reusable warmer lesscomfortable and more difficult to use. Users of the reusable warmersprefer relatively flexible containers made of relatively thin materialssuch as polyethylene and nylon (i.e., low cost, non vinyl packages). Themore flexible the warmer, the better the contact between the warmer andthe body part to be treated; however, when such thin materials are used,the super-cooled solution migrates even more, further accentuating theproblem of saddlebagging.

The saddlebagging problem cannot be readily solved by conventionalmeans, as, for example, by weld placement. Adding welds also results ina less flexible and more expensive product.

A need therefore exists for a reusable warmer of the.[.supercooled-solution type,.]. .Iadd.super-cooled solution-type.Iaddend.which eliminates or minimizes saddlebagging.

The prior art warmers also suffer from another substantial problem.Although present-day, reusable warmers tend to saddlebag whileunactivated, once the super-cooled solution is activated andcrystallization proceeds, the converse problem is presented. During theperiod from activation, through crystallization, to final cooling,present-day, .[.reusable-warmers.]. .Iadd.reusable warmers .Iaddend.gothrough a transition from water-like consistency to that of a hard,solid lump. As the phase transition proceeds, the reusable warmerbecomes more and more inflexible and difficult to shape or maintain inother than a flat configuration.

The phenomenon of hardening during the heat cycle makes it extremelydifficult to maintain present-day heat packs in contact with, forexample, a part of the human body such as an ankle, which is not flat.Of course, if the heat pack does not stay in contact with the region tobe treated, it is of no use.

From the foregoing it is clear that a need exists for a reusable warmerof the .[.supercooled solution-type,.]. .Iadd.super-cooled solution-type.Iaddend.that maintains a substantial degree of flexibility during itsuseful heat cycle.

Yet another problem associated with the present-day, reusable warmers ofthe .[.supercooled.]. .Iadd.super-cooled .Iaddend.solution-type is thattheir heat is generated over a fairly short period of time afteractivation. Accordingly, an abrupt increase to a peak temperature isreached within only a very few minutes after activation. The warmer thenimmediately thereafter begins an abrupt decline in temperature. For theuser, this translates into a high initial temperature followed by acooling in a short period of time to a temperature less than desired fortreating the afflicted area.

The problem, then, with the prior art warmers is that they reach a peaktemperature abruptly and then immediately begin to cool quickly. A needtherefore exists for a reusable warmer of the .[.supercooled solutiontype.]. .Iadd.super-cooled solution-type .Iaddend.having a moresustained period of time during which the heat pack remains within atherapeutically useful temperature range.

SUMMARY OF THE INVENTION

The present invention provides reusable warmers of the supersaturatedsolution type that are substantially free of saddlebagging. Further, thepresent invention provides warmers that exhibit a more sustained periodof time during which the heat pack remains within a therapeuticallyuseful temperature range. The reusable warmers of the present inventionalso maintain a substantial degree of flexibility during their usefulheat cycle.

It has now been found that all of the aforementioned problems associatedwith the prior art warmers may be overcome or minimized by incorporatinga sufficient amount of a gelling agent to gel the salt solution. Forexample, a small amount of a viscosity increasing agent may be employed,such as, for example, CELLOSIZE HEC-QP 52000-H gelling agent (UnionCarbide Corporation).

The present invention thus provides a reusable warmer comprising aflexible container, and located within said container, a.[.supercooled.]. .Iadd.super-cooled .Iaddend.salt solution, anactivator for initiating crystallization of said super-cooled saltsolution, and a gelling agent, said gelling agent being present insufficient quantity to convert said salt solution to a gel.

The viscosity .[.increasing, or gelling agent.]. .Iadd.increasing agentor gelling .Iaddend.agent makes the super-cooled sodium acetate solutionviscous enough to delay, prevent .Iadd., .Iaddend.or inhibit the naturaltendency of the solution to flow around body parts which are not flat,yet allows the reusable warmer to be flexible enough so that it readilyconforms to the contours of the body part to which it is being applied,making the reusable warmer more comfortable and easier to use.

Of great surprise is the fact that the use of the gelling agent alsocauses the product, after activation, to convert to a solid that is moreflexible than that of the prior art. Advantageously, then, the heatpacks of the present invention are capable of being maintained in closercontact with irregularly shaped body parts during their heat cycle, thanare those heat packs of the prior art.

Also of surprise is the fact that the incorporation of the gelling agentcauses a shift in the heat cycle to occur, lengthening the duration ofthe useful period that heat emanates from the heat pack, when comparedwith otherwise identical heat packs.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides improved reusable warmers, such as thosecontaining super-cooled sodium acetate solution, and an activator(sometimes called a "trigger"). The improved warmers include asufficient amount of a gelling agent to cause gelling of the sodiumacetate or other salt solution, as by incorporating a small amount ofthe gelling agent (sometimes referred to as "viscosity increasing" or"thickening agents") in the super-cooled sodium acetate solution duringthe manufacture of the reusable warmer, which amount is sufficient tosubstantially inhibit the flow of the salt solution, particularly afterit has been activated and is in the warm state. The exact type ofviscosity increasing, gelling or thickening agent is not critical to thepresent invention and any number of commercially available viscosityincreasing agents may be employed without departing from the spirit andscope of the invention.

The gelling agents utilized in the subject compositions can be any agentwhich creates a stable gel matrix, or otherwise essentially preventsflow, in the presence of substantial quantities of dissolved salt, suchas sodium acetate. For example, the resultant product may be technicallyregarded as a pseudoplastic, but for purposes of the present inventionwill be considered to be a gel. Thus, to be useful in the presentinvention it is not necessary for a conventional gel to be formed. Theuseful gelling agents also include what may be technically categorizedas viscosifiers and rheological control agents.

Thus, as use herein the term "gelling agent" includes conventionalgelling agents, those materials which, upon contact with water, imbibethe water and thereby form hydrogels or pseudoplastics, as well assuperabsorbants, which essentially prevent flow. Gelling agents of usein the present invention include both natural and synthetic materials.

Cellulose derivatives are particularly useful as gelling agents in thepresent invention, such as cellulose ethers, including methylcellulose,hydroxypropyl cellulose, methylhydroxypropyl cellulose, polypropylcellulose, carboxymethyl cellulose, hydroxyethyl cellulose,hydroxymethyl cellulose, carboxymethylhydroxyethyl cellulose,hydroxypropylmethyl cellulose, hydroxyethyl propylcellulose, andhydroxybutyl methylcellulose. Examples of superabsorbants useful asgelling agents in the practice of the present invention, which actuallyabsorb liquid and can absorb up to 1000 times their weight of water, arestarch graft copolymers, such as hydrolyzed acrylonitrile graftedstarch, and polyacrylate grafted .[.starch,..]. .Iadd.starch..Iaddend.U.S. Pat. Nos. .[.4,435,488;.]. .Iadd.4,435,488,.Iaddend.4,455,358, and 4,563,404, all of which are incorporated hereinby reference, disclose gelling agents of the type contemplated for suchuse herein .[.and the these patents are incorporated herein byreference.]..

Natural and synthetic gums and gum-like materials may also be employedas gelling agents in the present invention, such as Irish moss, gumtragacanth, Viscarin GMC, Kapa- and Iota carrageenan, sodium alginate,guar, hydroxypropyl guar, carboxymethyl-hydroxy-propyl guar, hydroxyethyl guar, alginates, carrageenan, xanthan gum, gelatin, agarose, gumarabic, carob, tragacanth, locust bean gum karaya, pectin, agar, gumacacia, tara gum, polysuccrose, polyglucose, and Zooglan (theexocellular polysaccharide isolated from Zoogloearamigera.Iadd.).Iaddend..

The gelling agents also may be any synthetic polymer or copolymer whichis hydratable an cross-linkable in solution, such as polymers whichcontain one or more of the following functional groups: hydroxyl,cishydroxyl, carboxyl, sulfate, sulfonate, amino or amide. Examples ofthese synthetic polymers include, but are not limited to, polyacrylates,polymethylacrylates, polyacrylamides, acrylamide methyl propane sulfonicacid copolymers, polyvinyl alcohols, maleic anhydride-based copolymerssuch as poly(methylvinylethermaleic anhydride), ethylene maleicanhydride, .[.and.]. maleic anhydride methylvinyl ether copolymers,polyvinyl pyrollidone, polyvinyl alcohol, polyacrylic acid, copolymersof acrylic acid and a polyallyl sucrose such as Carbomer 934, also knownas Carbopol 934 and available from B. F. Goodrich Chemical Company,polyoxyethylene-polyoxypropylene diol block copolymers which arecommercially available as the Pluronics from BASF-Wyandotte.[...]..Iadd., .Iaddend.carboxypolymethylene, and polyacrylamide.

Other suitable gelling agents may be selected by reference to publishedliterature, such as the Kirk-Othmer Encyclopedia of Chemical Technology,Vol. 20, 207-230, dealing with water soluble resins, which text isincorporated herein by reference.

One preferred class of gelling agents are the poly(ethylene oxide)polymers, such as those supplied under the trademark POLYOX by UnionCarbide Corporation.

Another example of a particularly well-suited type of gelling agent isthat sold by Union Carbide Corporation under the trademark CELLOSIZE.They are hydroxyethyl cellulose (HEC) gelling agents which are nonionic,water-soluble polymers. As indicated above, other water-soluble naturalpolymers (such as the gums, starches, celluloses, gelatin, etc.) andother chemically modified derivatives of the same which are commonlyused as thickeners, suspending agents, gelling agents, emulsifiers ordispersants may also be employed, provided that the material causes thesolution to gel or increase in viscosity sufficiently to inhibit orslow-down the flow of the solution during the heat producing phase.

The method of making a reusable warmer is well known and does not forman essential part of the herein-described invention. Any of severalmethods of manufacture can be employed as, for example, that which isdescribed in the aforementioned U.S. Pat. No. 4,077,390 at columns 2 and3. Further, the type of activator used also is not an essential part ofthe present invention and any suitable activator or trigger can be used,as, for example, the activators described in the aforementioned U.S.Pat. No. 4,077,390 or 4,872,442.

The essential element is the incorporation of a sufficient amount of agelling agent to cause the supercooled sodium acetate solution to form agel, such as a small amount of a viscosity increasing agent (such as,for example, Union Carbide's CELLOSIZE gelling agent), duringmanufacture of the reusable warmer. The amount of viscosity increasing,thickening or gelling agent used can vary depending upon the specifictype of reusable warmer being made. However, the amount used should notbe so small that the viscosity of the super-cooled sodiumacetate-solution is so low that the solution flows to an appreciableextent and collects in low spots in the bag (and cause saddle bagging),nor should it be so great that the viscosity of the super-cooledsolution is so high that the reusable warmer is not flexible and,therefore, not comfortable to use. Thus, when reference is made hereinto a gel, the term is to be understood as meaning a soft gell whichremains deformable.

It has been found that when hydroxyethyl cellulose is used as theviscosity increasing agent, the amount of gelling agent used can be lessthan about 5% by weight of the .[.supercooled.]. .Iadd.super-cooled.Iaddend.solution and, preferably, between about 1 to 4% by weight. Ofcourse, as is true with all polymeric materials, there is a relationshipbetween the molecular weight of the polymer and its viscosity or abilityto form a gel in solution.

With respect to CELLOSIZE HEC, it is preferable to use those grades withthe higher molecular weights, such as grades QP 52000 or 100 MH, whichhave the highest molecular weight. When such grades are used, the amountemployed will be less than if the lower molecular weight grades areused. Reference to the published manufacturer's literature regarding therelationship between the different grades and their viscosity as 1%aqueous solutions may be made to assist in determining optimum levels ofuse.

The salt used to form the .[.supercooled.]. .Iadd.super-cooled.Iaddend.solution may be any of the art-recognized salts which arecapable of forming a .[.supercooled.]. .Iadd.super-cooled.Iaddend.solution. The preferable salt is sodium acetate because it isrelatively inexpensive and innocuous. The amount of sodium acetate isnot critical. In general, the amount of sodium acetate will range fromabout 40 to about 50 percent.

The construction of the container also is not critical. Typically thecontainer will be in the shape of a bag and will be constructed of anysuitable material. Transparent films, which may be multiaminates, arepreferred. The films preferably have at least one side that may beheat-sealed. It is preferred to use nylon-polyethylene laminate as theflexible film.

The invention can further be best described by the following examples.

EXAMPLE 1

Into an empty vinyl bag sealed along three sides, there was introduced a50% sodium acetate solution at 200 degrees Fahrenheit containing 3percent, by weight, CELLOSIZE HEC-52000-H (Union Carbide Corporation),in an amount sufficient to fill the bag, and an activator of the typegenerally described in U.S. Pat. No. 4,872,442. The bag was then totallysealed and allowed to cool at ambient temperature over a period of abouttwo (2) hours. The cooling time could be reduced by immersion of thewarmer in cold water or by placing it in a refrigerator. After the twohours a viscous super-cooled sodium acetate solution formed which wasgelatinous in nature. The gelatinous super-cooled solution was generallyclear and transparent and the activator inside the reusable warmerreadily could be seen.

When the reusable warmer was activated (by flexing the activator) itprovided the same level of warmth for the same period of time as didsimilar reusable warmers which did not contain any CELLOSIZE HEC-QP52000-H. The thickened or gelatinous .[.supercooled.]..Iadd.super-cooled .Iaddend.sodium acetate solution was stable (it didnot separate into its component parts) and did not attack the container.The concentration of the super-cooled salt solution can be varieddepending on the temperature to be achieved by activation. It was foundthat the gelatinous super-cooled solution cushioned and suspended theactivator so that the danger of accidental activation duringmanufacture, shipping or storing of the reusable warmer wassubstantially reduced.

EXAMPLE 2

A reusable warmer was assembled similar to the one in Example 1, except2 to 3% by weight of CELLOSIZE HEC-QP 100000-H (Union CarbideCorporation) was employed instead of the CELLOSIZE HEC-QP 52000-H usedin Example 1. As in Example 1, a viscous super-cooled sodium acetatesolution formed which was gelatinous in nature. The gelatinoussuper-cooled solution was generally clear and transparent and theactivator inside the reusable warmer readily could be seen.

When the reusable warmer was activated (by flexing the activator) itprovided the same level of warmth for the same period of time as did.[.similar.]. the reusable warmer of Example 1. The thickened orgelatinous super-cooled sodium acetate solution was stable (it did notseparate into its component parts) and did not attack the container.

EXAMPLE 3

A reusable warmer was assembled similar to the one in Example 1, exceptthat between 10-30% by weight of a corn starch was used as the viscosityincreasing agent. During assembly of the reusable warmer, considerablecare must be taken in mixing in the starch because it tended to formlumps easily. Mixing was performed using high shear mixers. Theassembled reusable warmer, after heating, was not as clear as thereusable warmers of Examples 1 to 2. However, its stability was good.

The reusable warmer of the present invention can be used as a "coldpack" by placing it in a refrigerator for a short period. It is apparentthat the salt (sodium acetate) contained in the cold pack sufficientlyreduces the freezing temperature of the water so that freezing does nottake place. When used in this fashion the cold pack has many of the sameadvantages that it has when used as a reusable warmer, it holdstemperature well and conforms to the area of the body to which it isapplied. The stability of the cold pack when used in this fashion ishighly dependent on the purity of the water and the acetate used in itsmanufacture; the greater the purity of the solution, the lower thetemperature at which the cold pack can be used. For temperatures down to25 degrees Fahrenheit tap water and standard.[., .]. acetate .[.is.]..Iadd.are .Iaddend.acceptable.

EXAMPLE 4

To compare the temperature-time relationship during the heating cyclebetween a reusable warmer of the present invention having a gellingagent and one of the prior .Iadd.art .Iaddend.not employing a gellingagent, the following experiment was conducted.

One set of three inch by four inch bags were filled with two ounces ofgel solution made in accordance with Example 2 and another set werefilled with two ounces of solution identical to the first set, but notcontaining a gelling agent. Both sets of bags had initial startingtemperatures of 81° F. and were activated, attaining peak temperaturesof 107° F. An infrared thermometer was then used to measure surfacetemperatures every two minutes, for a period of twenty minutes. Duringthis time the bags containing the gelling agent were two-three degreeswarmer at all times than the bags that did not contain a gelling agent.The foregoing demonstrates that the reusable warmers of the presentinvention demonstrates a more desirable heat profile duringcrystallization, than the reusable warmers of the prior art.

EXAMPLE 5

The compare the flexibility, during the heating cycle, and at the endthereof, between a reusable warmer of the present invention having agelling agent and one of the prior not employing a gelling agent, thefollowing experiment was conducted.

The same sets of bags as employed in Example 4 were tested for theirability to conform to and hold a shape during the heating cycle, byplacing the bags around a 0.75 inch diameter dowl rod. The bagscontaining the gelling agent held their shape considerably better thanthe bags that did not contain the gelling agent. It was also found thatthe bags containing the gelling agent remained relatively stationarythroughout the wrapping and draping process, whereas the bags that didnot contain the gelling agent did not. The bags containing the gellingagent also had a cushion-like feel and response whereas the bags thatdid not contain the gelling agent had no "body" to them at all.

The wrapping and draping around the dowl rod simulates procedures thatwould be performed in a hospital setting. Thus, the foregoingdemonstrates that the reusable warmers of the present inventiondemonstrate better flexibility during and after crystallization, whencompared to the reusable warmers of the prior art.

It will be apparent to those skilled in this art that various changesmay be made in the construction and form of the reusable warmeremploying a gelatinous super-cooled solution and in the details of themethod of manufacture without departing from the spirit and scope ofthis invention, and that the specific directions and forms shown hereinare presented for the purpose of making an understandable disclosure ofthe invention and are not intended to be any restriction on the scopethereof, other than as defined in the accompanying claims.

EXAMPLE 6

To demonstrate the utility of the natural and synthetic gums as gellingagents used in the present invention, the following experiment usingxanthan gum was conducted.

To several three inch by four inch bags containing a premixed sodiumacetate solution, five percent, by weight, xanthan gum (supplied byKelco) was added. After addition of the xanthan gum, the solution gelledvery well, however, the color was extremely dark, forming an almostbrown, opaque composition. The bags were subsequently activated andperformed similarly to the bags of Example 4 containing the gellingagent.

What is claimed is:
 1. A reusable warmer comprising a flexiblecontainer, and located within said container, a .[.supercooled.]..Iadd.super-cooled salt .Iaddend.solution of sodium acetate, anactivator for initiating crystallization of said .[.supercooled.]..Iadd.super-cooled salt solution of sodium acetate, and a gelling agent,said gelling agent being present in sufficient quantity to convert saidsalt solution to a gel which remains deformable after crystallization ofsaid salt solution.
 2. The reusable warmer of claim 1 wherein thegelling agent is a non-ionic, water-soluble hydroxyethylcellulosepolymer.
 3. The reusable warmer of claim 1 wherein the gelling agent isselected from the group consisting of cellulose ethers.
 4. The reusablewarmer of claim 3 wherein the gelling agent is selected from the groupconsisting of methylcellulose, hydroxypropyl cellulose,methylhydroxypropyl cellulose, polypropyl cellulose, carboxymethylcellulose, hydroxyethyl cellulose, .[.and.]. hydroxymethyl cellulose,carboxymethylhydroxyethyl cellulose, hydroxypropylmethyl cellulose,hydroxyethyl propylcellulose, and hydroxybutyl methylcellulose.
 5. Thereusable warmer of claim 1 wherein the gelling agent is selected fromthe group consisting of starch graft copolymers.
 6. The reusable warmerof claim 1 wherein the gelling agent is selected from the groupconsisting of natural and synthetic gums.
 7. The reusable warmer ofclaim 6 wherein the gelling agent is selected from the group consistingof Irish moss, gum tragacanth, viscarin GMC, kappa- and iotacarrageenan, sodium alginate, guar, hydroxypropyl guar,carboxymethyl-hydroxypropyl guar, hydroxy ethyl guar, alginates,carrageenan, xanthan gum, gelatin, agarose, gum arabic, carob,tragacanth, locust bean gum, karaya, pectin, agar, gum acacia, tara gum,polysucrose, polyglucose, and zooglan.
 8. The reusable warmer of claim 1wherein the gelling agent is selected from the group consisting ofsynthetic polymers and copolymers which are hydratable andcross-linkable in solution.
 9. The reusable warmer of claim 8 whereinthe gelling agent is selected from the group consisting ofpolyacrylates, polymethylacrylates, polyacrylamides, acrylamide methylpropane sulfonic acid copolymers, polyvinyl alcohols, maleicanhydride-base copolymers, polyvinyl pyrollidone, polyvinyl alcohol,polyacrylic acid, copolymers of acrylic acid and a polyallyl sucrose,polyoxyethylene-polyoxypropylene diol block copolymers.Iadd.,.Iaddend.carboxypolymethylene, and polyacrylamide.
 10. The reusablewarmer of claim 1 wherein the gelling agent is selected from the groupconsisting of poly(ethylene oxide) polymers.
 11. The reusable warmer ofclaim 1, wherein said sodium acetate is present in an amount of fromabout 40% to about 50% by weight.
 12. The reusable warmer of claim 1,wherein said sodium acetate is present in an amount of about 40% byweight.
 13. The reusable warmer of claim 1, wherein said sodium acetateis present in an amount of about 50% by weight. .Iadd.
 14. A heat packcomprising a flexible container, a super-cooled salt solution comprisinga salt and a solvent located within said flexible container, anactivator for initiating crystallization of said salt solution, and agelling agent in sufficient quantity to convert said salt solution to agel such that said gel remains deformable after crystallization of saidsalt solution. .Iaddend..Iadd.15. The heat pack of claim 14, whereinsaid gelling agent is a nonionic, water-soluble hydroxyethylcellulosepolymer. .Iaddend..Iadd.16. The heat pack of claim 14, wherein saidgelling agent is a cellulose ether. .Iaddend..Iadd.17. The heat pack ofclaim 16, wherein said gelling agent is selected from the groupconsisting of methylcellulose, hydroxypropyl cellulose,methylhydroxypropyl cellulose, polypropyl cellulose, carboxymethylcellulose, hydroxyethyl cellulose, hydroxymethyl cellulose,carboxymethylhydroxyethyl cellulose, hydroxypropylmethyl cellulose,hydroxyethyl propylcellulose, and hydroxybutyl methylcellulose..Iaddend..Iadd.18. The heat pack of claim 14, wherein said gelling agentis a starch graft copolymer. .Iaddend..Iadd.19. The heat pack of claim14, wherein said gelling agent is a natural or synthetic gum. .Iadd.20.The heat pack of claim 19, wherein said gelling agent is selected fromthe group consisting of Irish moss, gum tragacanth, viscarin GMC, kappa-and iota-carrageenan, sodium alginate, guar, hydroxypropyl guar,carboxymethyl-hydroxypropyl guar, hydroxy ethyl guar, alginates,carrageenan, xanthan gum, gelatin, agarose, gum arabic, carob,tragacanth, locust bean gum, karaya, pectin, agar, gum acacia, tara gum,polysuccrose, polyglucose, and zooglan. .Iaddend..Iadd.21. The heat packof claim 14, wherein said gelling agent is a synthetic polymer orcopolymer which is hydratable and cross-linkable in solution..Iaddend..Iadd.22. The heat pack of claim 21, wherein said gelling agentis selected from the group consisting of polyacrylates,polymethyacrylates, polyacrylamides, acrylamide methyl propane sulfonicacid copolymers, polyvinyl alcohols, maleic anhydride-based copolymers,polyvinylpyrollidone, polyvinyl alcohol, polyacrylic acid, copolymers ofacrylic acid and a polyallyl sucrose, polyoxyethylene-polyoxypropylenediol block copolymers, carboxypolymethylene, and polyacrylamide..Iaddend..Iadd.23. The heat pack of claim 14, wherein said gelling agentis a poly(ethylene oxide) polymer. .Iaddend..Iadd.24. The heat pack ofclaim 14, wherein said salt is sodium acetate. .Iaddend..Iadd.25. Theheat pack of claim 24, wherein said sodium acetate is present in saidsalt solution in an amount of from about 40% to about 50% by weight..Iaddend..Iadd.26. The heat pack of claim 24, wherein said activator islocated within said flexible container. .Iaddend..Iadd.27. The heat packof claim 25, wherein said sodium acetate is present in said saltsolution in an amount of about 40% by weight. .Iaddend..Iadd.28. Theheat pack of claim 25, wherein said sodium acetate is present in saidsalt solution in an amount of about 50% by weight. .Iaddend..Iadd.29.The heat pack of claim 25, wherein said activator is located within saidflexible container. .Iaddend..Iadd.30. The heat pack of claim 14,wherein said activator is located within said flexible container..Iaddend.